This invention is an improvement in photographic printers used to make film or paper prints from either negative or positive color film transparencies. The usual object of photographic printing is to duplicate, as nearly as possible, the subject matter contained in the original. Scanning Cathode Ray Tube (CRT) printers have been widely used for many years to vary image contrast, by means of unsharp luminous masking, during exposure of the photographic reproduction. A scanning spot of light is employed because CRT beam intensity can easily be modified to provide instantaneous contrast control at any point within the printing stage format. CRT printers heretofore have not, however, been widely used for color printing because the light output obtainable from such a source has not been sufficient to provide photographic reproductions within commercially-acceptable exposure times. A printer employing a conventional shadow mask color CRT for example, might dissipate up to eighty percent of its electron beam power in the shadow mask structure, leaving a maximum of twenty percent for conversion to light useful for the color exposing process. Until now, a reversal color print made with a blended-phosphor CRT light source and relatively slow duplicating material has required an exposure time of between 5 and 30 minutes, depending upon the density of the original, which is unacceptable by most standards.
This invention is particularly adapted to work with current color print film or paper such as Eastman Kodak Aerochrome duplicating film Type 2447; Eastman Kodak Aerial Color Negative film, Type SO 149; Kodak 2203 RC print paper; Ciba-Geigy's Cibachrome color print paper, and similar materials. These particular emulsions are photographically slow when compared to conventional black and white printing materials and, moreover, are essentially opaque to transmitted light throughout most of the visible spectrum.
When trying to duplicate an original film as closely as possible, a contact printing process is normally preferred because of its higher speed and superior resolution, despite the fact that there may be a substantial gain in image contrast. Conversely, when printing by projection, the lens may be a source of image degradation, reduced contrast, and light loss, all of which can be avoided in a contact system. Scanning CRT printers frequently employ light transmitted through the raw stock to control the exposure level and/or contrast of the duplicating process, but this is extremely difficult with the aforementioned color reproduction materials, inasmuch as they transmit so little visible light.
The present invention is particularly well adapted for use with opaque color print film and paper materials, in a contact printing configuration, and is capable of providing automatic exposure level control and automatic modification of the image contrast range to fit within the contrast acceptance range of the receiving media.